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Carbon‐Centered Radical Addition and β‐Scission Reactions: Modeling of Activation Energies and Pre‐exponential Factors
Author(s) -
Sabbe Maarten K.,
Reyniers MarieFrançoise,
Van Speybroeck Veronique,
Waroquier Michel,
Marin Guy B.
Publication year - 2008
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200700469
Subject(s) - chemistry , basis set , steric effects , computational chemistry , thermodynamics , ab initio , reaction rate constant , reaction rate , additive function , ab initio quantum chemistry methods , molecule , density functional theory , kinetics , stereochemistry , organic chemistry , mathematics , physics , quantum mechanics , mathematical analysis , catalysis
A consistent set of group additive values ΔGAV° for 46 groups is derived, allowing the calculation of rate coefficients for hydrocarbon radical additions and β ‐scission reactions. A database of 51 rate coefficients based on CBS‐QB3 calculations with corrections for hindered internal rotation was used as training set. The results of this computational method agree well with experimentally observed rate coefficients with a mean factor of deviation of 3, as benchmarked on a set of nine reactions. The temperature dependence on the resulting ΔGAV°s in the broad range of 300–1300 K is limited to ±4.5 kJ mol −1 on activation energies and to ±0.4 on log A (A: pre‐exponential factor ) for 90 % of the groups. Validation of the ΔGAV°s was performed for a test set of 13 reactions. In the absence of severe steric hindrance and resonance effects in the transition state, the rate coefficients predicted by group additivity are within a factor of 3 of the CBS‐QB3 ab initio rate coefficients for more than 90 % of the reactions in the test set. It can thus be expected that in most cases the GA method performs even better than standard DFT calculations for which a deviation factor of 10 is generally considered to be acceptable.